1. Field of the Invention
Embodiments of the present invention relate to electrolytic chemical mechanical polishing. More particularly, embodiments of the present invention relate to an electrolyte solution for copper removal and a method for removing copper ions therefrom.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, as the limits of circuit technology are pushed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
Multilevel interconnects are formed using sequential material deposition and material removal techniques on a substrate surface to form features therein. As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization prior to further processing. Planarization or “polishing” is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing excess deposited material and removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials to provide an even surface for subsequent lithography and processing.
Electrochemical mechanical polishing (ECMP) is one method of planarizing a surface of a substrate. ECMP removes conductive materials from a substrate surface by electrochemical dissolution while polishing the substrate with a reduced mechanical abrasion compared to conventional chemical mechanical planarization (CMP) processes. A typical ECMP system includes a substrate support and two electrodes disposed within an electrolyte containment basin. In operation, metal atoms on a surface of a substrate are ionized by an electrical current from a source of potential, such as a battery or other voltage source connected to the two electrodes. The metal ions dissolve into the surrounding electrolyte solution at a rate proportional to the electric current. The metal ions from the substrate (anode) either plate the electrode (cathode), fall out of the solution as a precipitate, or remain in the solution. The destiny of the metal ions depends greatly on the chemistry of the metals and the solution.
One problem associated with ECMP techniques is safely handling the conventional electrolyte solution. A conventional electrolyte solution typically contains various performance enhancing additives and electrolytes. Common electrolytes contain strong acids having a pH less than or about 1.0, such as sulfuric acid and phosphoric acid, for example. These acidic electrolytes are corrosive and are difficult to handle safely.
Highly acidic electrolytes also interfere with additives of the electrolyte solution, thereby inhibiting or canceling the beneficial effects of the additive. In particular, metal ions from the substrate tend to chemically bond to the certain additives which alters the reactive or chemical characteristics of the additive. One common solution is to add more of the depleted additive. However, this approach is difficult to control or regulate in a continuous processing system. Additionally, the amount of additive to be added is difficult to quantify since the rate of depletion is dependent on several processing parameters that are difficult to monitor and quantify.
There is a need, therefore, for an electrolyte composition containing less hazardous components and less acidic components. There is also a need for a method of continously using an electrolyte composition.